U.S. patent number 5,403,436 [Application Number 08/272,519] was granted by the patent office on 1995-04-04 for plasma treating method using hydrogen gas.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Shuzo Fujimura, Yuji Matoba, Takeshi Miyanaga, Yoshimasa Nakano, Tetsuya Takeuchi.
United States Patent |
5,403,436 |
Fujimura , et al. |
April 4, 1995 |
Plasma treating method using hydrogen gas
Abstract
A plasma treating method subjects an object surface to a plasma
treating within a chamber. First, first and second gasses are
supplied into the chamber, where the first gas includes hydrogen
molecules as a main component, the second gas includes a quantity
of hydrogen less than that included in the first gas and is
selected from a group of materials consisting of organic compounds
and inorganic compounds, the organic compounds include hydrogen and
oxygen and the inorganic compounds include hydrogen. Second, plasma
of a mixed gas which is made up of the first and second gasses is
generated within the chamber to subject the object surface to the
plasma treating. Preferably, the second gas is water vapor.
Inventors: |
Fujimura; Shuzo (Tokyo,
JP), Takeuchi; Tetsuya (Koube, JP),
Miyanaga; Takeshi (Ono, JP), Nakano; Yoshimasa
(Akashi, JP), Matoba; Yuji (Koube, JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
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Family
ID: |
15876738 |
Appl.
No.: |
08/272,519 |
Filed: |
July 11, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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93906 |
Jun 30, 1993 |
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719738 |
Jun 25, 1991 |
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Foreign Application Priority Data
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Jun 26, 1990 [JP] |
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2-168905 |
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Current U.S.
Class: |
216/69; 216/79;
257/E21.225; 257/E21.226; 257/E21.256; 257/E21.3; 427/534; 427/536;
427/539; 438/694; 438/725 |
Current CPC
Class: |
C23C
16/0245 (20130101); G03F 7/36 (20130101); G03F
7/40 (20130101); H01L 21/02046 (20130101); H01L
21/02085 (20130101); H01L 21/31138 (20130101); H01L
21/321 (20130101) |
Current International
Class: |
C23C
16/02 (20060101); G03F 7/36 (20060101); G03F
7/40 (20060101); H01L 21/02 (20060101); H01L
21/306 (20060101); H01L 21/311 (20060101); H01L
21/321 (20060101); B05D 003/06 (); H01L
021/306 () |
Field of
Search: |
;427/525,526,535,536,534,539 ;156/643,646,662,664,668 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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62-154627 |
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Jul 1987 |
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JP |
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1-192119 |
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Aug 1989 |
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JP |
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Other References
Patent Abstracts of Japan, vol. 4, No. 170 (E-35) (652) 22 Nov.
1980, and JP-A-55 117244 Kobayashi. .
Patent Abstracts of Japan, vol. 13, No. 402 (C-633) 06 Sep. 1989,
and JP-A-01 145396 Takeuchi. .
"Low-Temperature Surface Cleaning Method Using Low-Energy Reactive
Ionized Species", Yamada, J. Appl. Phys. 65 (2), Jan. 15, 1989, pp.
775-781. .
Patent Abstracts of Japan, vol. 10, No. 355 (C-388) 29 Nov. 1986,
and JP-A-61 153277 Toyoshima Yasutake. .
Patent Abstracts of Japan, vol. 7, No. 190 (E-194) (1335) 19 Aug.
1983, and JP-A-58 093251 Hazuki. .
Patent Abstracts of Japan, vol. 14, No. 194 (E-919) 20 Apr. 1990,
and JP-A-02 039524 Zenichi. .
Patent Abstracts of Japan, vol. 9, No. 160 (C-289) 04 Jul. 1985,
and JP-A-60 033300 Nobuaki. .
Patent Abstracts of Japan, vol. 13, No. 352 (E-801) (3700) 08 Aug.
1989, and JP-A-01 112734 Yano. .
Patent Abstracts of Japan, vol. 3, No. 82 (E-123) 14 Jul. 1979, and
JP-A-54 059881 Moritaka. .
Patent Abstracts of Japan, vol. 13, No. 509 (E-846) 15 Nov. 1989,
and JP-A-01 206624 Yuko. .
"Removal of a Thin SiO.sub.2 Layer by Low-Energy Hydrogen Ion
Bombardment at Elevated Temperature, Kiyoshi Miyake, Japanese
Journal of Applied Physics", vol. 28, No. 11, Nov. 1989, pp.
2376-2381. .
"Ashing of Ion-Implanted Resist Layer", Japanese Journal of Applied
Physics, vol. 28, No. 10, Oct. 1989, pp. 2130-2136, Fujimura et
al..
|
Primary Examiner: Padgett; Marianne
Attorney, Agent or Firm: Armstrong, Westerman, Hattori,
McLeland & Naughton
Parent Case Text
This application is a continuation of application Ser. No.
08/093,906, filed Jun. 30, 1993, which is a continuation of
application Ser. No. 07/719,738, filed Jun. 25, 1991, both now
abandoned.
Claims
What is claimed is:
1. A plasma etching method for plasma etching a resist layer on a
surface of an object within a chamber, said plasma etching method
comprising:
(a) coating the object surface with a resist layer;
(b) supplying an etching gas consisting of first and second gasses
into the chamber, said first gas consisting essentially of hydrogen
gas, said second gas consisting essentially of a quantity of
hydrogen less than that included in the first gas and being
provided in the form of water vapor; and
(c) irradiating said etching gas with microwaves to generate within
the chamber a plasma of said etching gas so as to subject the
resist layer on the object surface to the hydrogen plasma
etching.
2. The plasma etching method as claimed in claim 1, wherein a ratio
H.sub.2 O/(H.sub.2 +H.sub.2 O) of hydrogen (H.sub.2) and water
vapor (H.sub.2 O) included in the mixed gas is greater than 0 but
less than or equal to 30%.
3. The plasma etching method as claimed in claim 1, wherein said
irradiating step is carried out at a pressure of 1 Torr or
greater.
4. The plasma etching method as claimed in claim 1, wherein the
object surface is made of a material selected from a group
consisting of organic materials, semiconductors and metals.
5. The plasma etching method as claimed in claim 4, wherein the
object surface is made of an irradiated organic material.
6. The plasma etching method as claimed in claim 4, wherein said
irradiating step subjects the object surface which is made of
either one of semiconductor and metal to the plasma etching to
prepare the object surface for formation of a layer thereon.
7. The plasma etching method as claimed in claim 1, wherein the
object is a silicon substrate.
8. The plasma etching method as claimed in claim 1, wherein the
resist layer is a novolac resin system resist.
9. The plasma etching method as claimed in claim 3, wherein said
irradiating step is carried out at a pressure of 1.8 Torr or
greater.
10. The plasma etching method as claimed in claim 2, wherein the
ratio H.sub.2 O/(H.sub.2 +H.sub.2 O) of hydrogen (H.sub.2) and
water vapor (H.sub.2 O) included in the mixed gas is between
approximately 10% and approximately 30%.
11. The plasma etching method as claimed in claim 10, wherein the
ratio H.sub.2 O/(H.sub.2 +H.sub.2 O) of hydrogen H.sub.2 and water
vapor (H.sub.2 O) included in the mixed gas is approximately
20%.
12. The plasma etching method as claimed in claim 10, wherein said
etching gas consists solely of said hydrogen gas and water vapor.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to plasma treating methods,
and more particularly to a plasma treating method which uses a
hydrogen gas.
Various proposals have been made to carry out a plasma treating of
a solid surface using a gas which includes hydrogen. For example,
Fujimura et al., Procedures of The Symposium on Dry Process, Edited
by Nishizawa et al., PV 88-7, The Electromechanical Society, Inc.
1988, pp. 126-133 proposes a method of removing a resist layer
which is used as a mask during an ion implantation. On the other
hand, K. Miyake, "Removal of a Thin SiO.sub.2 Layer by Low-Energy
Hydrogen Ion Bombardment at Elevated Temperatures", Japanese
Journal of Applied Physics, Vol. 28, No. 11, November, 1989, pp.
2376-2381 proposes a method of cleaning a silicon surface using
hydrogen ions drawn out from the plasma. The present invention
relates to a plasma treating method which uses a hydrogen gas and
is applicable to the proposed methods described above.
For example, when using hydrogen in a pre-process which is carried
out before epitaxially growing a layer on a silicon substrate, this
pre-process is generally carried out by heating the substrate to a
high temperature within a hydrogen atmosphere. Because the process
uses a large quantity of hydrogen, the hydrogen is, for safety
reasons, usually diluted by a gas such as nitrogen gas and argon
gas which do not react with hydrogen. The pre-process using the
hydrogen is carried out mainly for the purpose of removing a
natural oxide layer which is formed on the silicon substrate, for
example. Safety precautions must be taken during this pre-process,
because the substrate temperature is raised to a high temperature
on the order of 1000.degree. C. and the hydrogen gas is supplied at
a rate of 10 to 1000 liters/minute.
Hence, M. Miyake referred above proposes the plasma treating which
can be carried out at a relatively low temperature, with an
improved safety and high efficiency. In addition, Fujimura et al.
referred above proposes the use of hydrogen plasma to remove ion
implanted resist.
According to the conventional plasma treating methods which use
hydrogen, the hydrogen gas itself is used, or a hydrogen gas which
is diluted by an inert gas or nitrogen gas is used. However, there
is a problem in that the ashing rate is poor and the process takes
too long a time for practical purposes.
The main object of the plasma treating is to utilize hydrogen ions
(H.sup.+) and hydrogen radicals (hydrogen atoms H). For this
reason, it is possible to employ an electron cycrotron resonance
(ECR) plasma in order to improve the dissociation of the hydrogen
and increase the speed of the process. However, it still takes a
relatively long time to carry out the process and the use of the
ECR plasma is still unsatisfactory for practical purposes.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to
provide a novel and useful plasma treating method in which the
problems described above are eliminated.
Another object of the present invention is to provide a plasma
treating method for subjecting an object surface to a plasma
treating within a chamber, comprising the steps of (a) supplying
first and second gasses into the chamber, where the first gas
includes hydrogen molecules as a main component, the second gas
includes a quantity of hydrogen less than that included in the
first gas and is selected from a group of materials consisting of
organic compounds and inorganic compounds, the organic compounds
include hydrogen and oxygen and the inorganic compounds include
hydrogen, and (b) generating within the chamber plasma of a mixed
gas which is made up of the first and second gasses to subject the
object surface to the plasma treating. According to the plasma
treating method of the present invention, it is possible to
considerably increase the speed of processes which use hydrogen
atoms and hydrogen ions.
Other objects and further features of the present invention will be
apparent from the following detailed description when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, 1B and 1C are cross sectional views for explaining a
first embodiment of a plasma treating method according to the
present invention;
FIG. 2 is a cross sectional view generally showing a plasma
treating apparatus used in the first embodiment;
FIG. 3 is a diagram showing an etching rate versus ratio of gas
added to hydrogen gas, for explaining the effects of the first
embodiment;
FIG. 4 is a diagram showing a sheet resistance versus RIE process
time for explaining the effects of a second embodiment of the
plasma treating method according to the present invention;
FIGS. 5A and 5B respectively are cross sectional views generally
showing apparatuses used in a third embodiment of the plasma
treating method according to the present invention;
FIG. 6 shows the relative concentration of hydrogen atoms in the
plasma when the hydrogen plasma process is carried out using only
hydrogen gas;
FIG. 7 shows the relative concentration of hydrogen atoms in the
plasma when the hydrogen plasma process is carried out using
hydrogen gas added with water vapor;
FIG. 8 shows the quantity change of hydrogen atoms with time when
the hydrogen plasma process is carried out using only hydrogen
gas;
FIG. 9 shows the quantity change of hydrogen atoms with time when
the hydrogen plasma process is carried out using hydrogen gas added
with water vapor; and
FIG. 10 shows the density of hydrogen atoms depending on the
quantity of water vapor added to the hydrogen gas when carrying out
the hydrogen plasma process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A description will be given of a first embodiment of a plasma
treating method according to the present invention, by referring to
FIGS.1 through 4. In this embodiment, the present invention is
applied to a resist removing process.
As shown in FIG. 1A, a resist layer 2 is formed on a 6-inch
diameter silicon (Si) substrate 1 by coating approximately 1 .mu.m
of novolac resin system resist such as the resist OFPR8600A
manufactured by Tokyo Ohka Kogyo of Japan. The substrate 1 coated
with the resist layer 2 is baked on a hot plate for 90 seconds at
90.degree. C., and thereafter, P.sup.+ ions are implanted with a
dosage of 1.times.10.sup.16 atoms/cm.sup.2 at 70 KeV. By this ion
implantation, a deteriorated layer 2b having a thickness on the
order of 2300 .ANG. covers a non-deteriorated layer 2a of the
resist layer 2. This deteriorated layer 2b is made up of a cross
contaminated layer 2c, an injection carbonization layer 2d and a
secondary carbonization layer 2e. The formation of the deteriorated
layer 2b is reported in Fujimura et al., "Ashing of Ion-Implanted
Resist Layer", Japanese Journal of Applied Physics, Vol. 28, No.
10, October 1989, pp. 2130-2136.
Next, a reactive ion etching (RIE) module 3 of the plasma treating
apparatus shown in FIG. 2 is used to remove the deteriorated layer
2b by hydrogen plasma as shown in FIG. 1B, and a downstream module
4 of the plasma treating apparatus is thereafter used to remove the
remaining non-deteriorated layer 2a by a downstream ashing so as
not to damage the substrate 1.
The RIE module 3 generally includes a substrate stage 5a on which
the substrate 1 is placed and a heater 6 provided within the stage
5a, and the stage 5a is provided within a plasma chamber 8. On the
other hand, the downstream module 4 generally includes a stage 5b,
a quartz window 9 and a shower-head 10. An arm 7 rotates in the
direction of an arrow to move the substrate 1 from the RIE module 3
to the downstream module 4. When moving the substrate 1 from the
RIE module 3, pins (not shown) of the stage 5a lift up the
substrate 1 so that the arm 7 can carry the substrate 1 to the
downstream module 4. At the downstream module 4, pins (not shown)
of the stage 5b receive the substrate 1 and then lower the
substrate 1 in position on the stage 5b.
If oxygen plasma is used to remove the deteriorated layer 2b, the
injected material is oxidized and remains as an oxide. Accordingly,
it is desirable to use a gas which does not include oxygen so that
the effects caused by the oxygen is negligible even when the Si of
the deteriorated layer 2b includes oxygen. In other words, it is
necessary to use a gas which results in a process approximately the
same as that obtained when only hydrogen gas is used.
The hydrogen plasma process, that is, the RIE process, is carried
out by supplying hydrogen gas to the plasma chamber 8 shown in
FIG.2 at a rate of 500 cc/minute, and exciting hydrogen using a
high-frequency wave of 13.56 MHz with a power of 450 W at 1 Torr so
as to generate the hydrogen plasma. The structure shown in FIG. 1A
is subjected to this hydrogen plasma process in the RIE module 3.
In addition, the downstream process is carried out in the
downstream module 4 by supplying oxygen (O.sub.2) gas at a rate of
600 cc/minute, supplying water (H.sub.2 O) at a rate of 400
cc/minute, using a microwave of 2.45 GHz with a power of 1 kW at 1
Torr, and setting the temperature of the stage 5b to 200.degree.
C.
When the hydrogen plasma process is insufficient, the deteriorated
layer 2b remains and this remaining deteriorated layer 2b cracks
and is scattered as unwanted contamination particles during the
downstream process due to the expansion of the non-deteriorated
layer 2a when the substrate 1 is heated. In most cases, the
contamination particles cannot be removed completely during the
downstream ashing, and the contamination remains on the substrate
1. Accordingly, it is possible to judge whether or not the hydrogen
plasma process is sufficient by determining whether or not the
deteriorated layer 2b cracks during the downstream process and
whether or not the contamination of the deteriorated layer 2b
remains on the substrate 1.
A minimum time required for the hydrogen plasma process to be
carried out in order to completely remove the deteriorated layer 2b
of the resist layer 2 was approximately 7 minutes. Next, when the
hydrogen plasma process was carried out at an increased pressure of
approximately 2 Torr, it took approximately 10 minutes to
completely remove the deteriorated layer 2b.
On the other hand, this embodiment was carried out under first and
second conditions described hereunder. Under the first condition,
the hydrogen plasma process was carried out by modifying the supply
of the hydrogen gas to a rate of 425 cc/minute, the supply of water
vapor to a rate of 75 cc/minute and the pressure to 1 Torr. In this
case, the minimum time required to completely remove the
deteriorated layer 2b of the resist layer 2 was approximately 90
seconds. Under the second condition, the hydrogen plasma process
was carried out by modifying the supply of the hydrogen gas to a
rate of 475 cc/minute, the supply of water vapor to a rate of 25
cc/minute and the pressure to 2 Torr. In this case, the minimum
time required to completely remove the deteriorated layer 2b of the
resist layer 2 was approximately 105 seconds.
Next, the hydrogen plasma process was carried out with respect to a
resist layer 2 which has a pattern such that the resist layer 2
occupies 1/2 the area on the substrate 1. Under one condition, the
hydrogen plasma process was carried out by supplying the hydrogen
gas at a rate of 450 cc/minute, supplying the water vapor at a rate
of 75 cc/minute and setting the pressure to 1 Torr. In this case,
the minimum time required to completely remove the deteriorated
layer 2b of this resist layer 2 was approximately 75 seconds. Under
another condition, the hydrogen plasma process was carried out by
supplying the hydrogen gas at a rate of 475 cc/minute, supplying
the water vapor at a rate of 25 cc/minute and setting the pressure
to 2 Torr. In this case, the minimum time required to completely
remove the deteriorated layer 2b of the resist layer 2 was
approximately 105 seconds. As a result, it may be regarded that the
process speed of the hydrogen plasma process has little dependency
on the pattern area of the resist layer 2.
In order to observe the effects of adding the water vapor to the
hydrogen gas in this embodiment, the etching rate of a resist layer
which has not been subjected to an ion implantation was observed as
indicated by a solid line in FIG. 3. The resist layer used was
coated on the entire surface of the substrate and baked at
200.degree. C. for one minute, and the RIE was carried out at a
pressure of 1 Torr with a microwave power of 1 kW. FIG.3 also shows
the etching rate of the resist layer using the hydrogen gas which
is added with nitrogen gas, as indicated by a dotted line. As may
be seen from FIG. 3, when the added water vapor is such that a
ratio H.sub.2 O/(H.sub.2 +H.sub.2 O) of the water vapor is
approximately 10%, the etching rate increases to approximately five
times that obtainable when no water vapor is added to the hydrogen
gas. On the other hand, the etching rate decreases when the ratio
of the water vapor exceeds 20%. The etching rate is approximately
constant when the ratio of the water vapor is greater than 50%, and
in this case, the etching rate is approximately 1/2 the maximum
etching rate shown in FIG. 3. The data shown in FIG. 3 were
obtained using the RIE module 3 shown in FIG. 2.
In addition, the color of the plasma was bluish pink when the ratio
of the water vapor is 50 to 100%, while the color of the plasma was
pink when the ratio of the water vapor is 0 to 30%. Hence, it was
presumed that the hydrogen plasma process becomes approximately the
same as an RIE process using 100% water vapor when the ratio of the
water vapor is 50 to 100%, and the hydrogen plasma process becomes
approximately the same as the RIE process using 100% hydrogen gas
when the ratio of the water vapor is 0 to 30%. In other words, when
ratio of the water vapor added to the hydrogen gas is 30% or less
but greater than 0, the etching rate of the hydrogen plasma process
can be increased to approximately five time that of the hydrogen
plasma process using hydrogen gas alone.
As may be seen from FIG. 3, the sputtering effect of the nitrogen
is obtainable when the nitrogen gas is added to the hydrogen gas
because nitrogen is heavier than hydrogen. However, the etching
rate does not increase over approximately two times the etching
rate obtainable when the hydrogen plasma process uses the hydrogen
gas alone.
Although not shown in FIG. 3, the etching rate did not change
greatly from that indicated by the dotted line even when argon gas
was added to the hydrogen gas when carrying out the hydrogen plasma
process.
Next, a description will be given of a second embodiment of the
plasma treating method according to the present invention. In this
embodiment, a silicon dioxide (SiO.sub.2) layer having a thickness
of 200 .ANG. is formed on a (100) face of a p-type single crystal
substrate. As.sup.+ ions were implanted into the substrate via the
SiO.sub.2 layer with a dosage of 4.times.10.sup.15 atoms/cm.sup.2
at a power of 70 keV. After removing the SiO.sub.2 layer, the
hydrogen plasma process was carried out. Then, an annealing process
was carried out at 1000.degree. C. for 30 minutes in a nitrogen
atmosphere.
When the pressure during the hydrogen plasma process (that is, the
RIE process) was varied and the sheet resistance was examined, it
was found that the sheet resistance decreases when the pressure is
increased from 0.5 Torr to 1 Torr. In FIG. 4, a curve Al shows the
sheet resistance at 1 Torr and a curve A2 shows the sheet
resistance at 0.5 Torr. In addition, a curve A3 shows the sheet
resistance for the case where the hydrogen plasma process was
carried out without removing the SiO.sub.2 layer, and in this case,
the sheet resistance was virtually constant. Hence, the As within
the Si escapes and the resistance increases when the pressure is
less than 1 Torr, but it is possible to prevent the As within the
Si from escaping and thus prevent the resistance from increasing
when the pressure is 1 Torr or greater. In addition, when the area
effect is considered, the desirable pressure is 1.8 Torr or greater
because the area effect can be suppressed in this case.
Next, a description will be given of a third embodiment of the
plasma treating method according to the present invention.
When epitaxially growing a Si layer on a Si substrate, there is a
need to remove a natural oxide layer and contaminating materials
such as carbon on the surface of the Si substrate. This embodiment
removes such natural oxide layer and contaminating materials using
apparatuses shown in FIGS. 5A and 5B.
FIG. 5A shows an epitaxial growth apparatus including a chamber
11a, a stage 12a and a heater 13a. On the other hand, FIG.5B shows
a plasma generating apparatus including a chamber 11b, a stage 12b
and a heater 13b.
First, the epitaxial growth apparatus shown in FIG. 5A is used to
grow a Si epitaxial layer having a thickness of 1 .mu.m. In order
to make the crystal defect in the Si epitaxial layer under 1
defect/cm.sup.2, a hydrogen thermal process was carried out at 1
Torr and 1000.degree. C. for 10 minutes. The flow rate of the
hydrogen gas was set to 15 liters/minute.
The plasma generating apparatus shown in FIG. 5B is connected to
the epitaxial growth apparatus shown in FIG. 5A, and plasma of
hydrogen was generated by setting the pressure to 1 Torr and the
flow rate of the hydrogen gas to 500 cc/minute. A downstream
pre-process was carried out using a gas which is dissociated by the
generated plasma. The downstream pre-process of 30 minutes was
required to make the crystal defect density to 1 defect/cm.sup.2 or
less. Next, when the flow rate of the hydrogen gas was set to 450
cc/minute and the flow rate of the water vapor was set to 50
cc/minute during the downstream pre-process, the crystal defect
density became 1 defect/cm.sup.2 or less in 10 minutes. In other
words, the speed of the downstream pre-process was increased by
reducing the flow rate of the hydrogen gas and adding a small
quantity of water vapor to the hydrogen gas.
The detailed mechanisms of the present invention has not yet been
elucidated. However, based on the experiments conducted by the
present inventors, it may be regarded that the density of the
hydrogen atoms increases because the dissociation of hydrogen
molecules is accelerated when water vapor is added to the hydrogen
gas during the hydrogen plasma process. In addition, it may be
regarded that the density of the hydrogen atoms increases because
the recombination of hydrogen atoms is suppressed by the addition
of the water vapor. Normally, during the hydrogen plasma process,
the recombination of the hydrogen atoms occurs mainly in the
vicinity of the wall of the chamber. It was confirmed that, when
the hydrogen plasma process is carried out using the hydrogen gas
alone, the recombination of the hydrogen atoms is substantially the
same even when the material used for the chamber wall is changed.
But when the material used for the chamber wall is changed and the
hydrogen plasma process is carried out using the hydrogen gas
combined with water vapor, it was confirmed that the recombination
of the hydrogen atoms changes depending on the chamber wall
material. Hence, it was indirectly found that the recombination of
hydrogen atoms is suppressed by the addition of the water
vapor.
FIG. 6 shows the relative concentration of hydrogen atoms in the
plasma (value of I.sub.H (4861.ANG.)/I.sub.Ar (8115.ANG.)) when the
hydrogen plasma process is carried out using only hydrogen gas. In
this case, the relative concentration of hydrogen atoms is 0.066.
On the other hand, FIG. 7 shows the relative concentration of
hydrogen atoms in the plasma (value of I.sub.H (4861.ANG.)/I.sub.Ar
(8115.ANG.)) when the hydrogen plasma process is carried out using
hydrogen gas added with water vapor. The ratio of the water vapor
is 40%, and in this case, the relative concentration of hydrogen
atoms is 0.314. In other words, when the hydrogen plasma process
uses hydrogen gas added with water vapor as in FIG. 7, the relative
concentration becomes approximately five times that of the case
shown in FIG. 6. Hence, these experimental results support the
above assumptions that the density of the hydrogen atoms increases
when water vapor is added to the hydrogen gas during the hydrogen
plasma process.
FIG. 8 shows the change in the intensity of hydrogen atoms with
time when the hydrogen plasma process is carried out using only
hydrogen gas. On the other hand, FIG. 9 shows the change in the
intensity of hydrogen atoms with time when the hydrogen plasma
process is carried out using hydrogen gas added with water vapor.
FIGS. 8 and 9 show the quantity of hydrogen atoms in a vicinity of
a position HP in FIG. 5B when the plasma of hydrogen is generated
using a microwave of 2.45 GHz with a power of 1.5 kW at a pressure
of 1 Torr. Further, the values shown in FIGS. 8 and 9 are
normalized and thus, the ordinates are in arbitrary units. FIG. 9
shows the case where the ratio of water vapor added to the hydrogen
gas is 20%. As may be seen by comparing FIGS. 8 and 9, the quantity
of hydrogen atoms decreases after generation of the plasma at a
time t=0 in FIG. 8, but the quantity of hydrogen atoms remains
substantially constant after generation of the plasma at the time
t=0 in FIG. 9. As a result, these experimental results support the
above assumptions that the recombination of hydrogen atoms is
suppressed by the addition of the water vapor.
FIG. 10 shows the density of hydrogen atoms depending on the
quantity of water vapor added to the hydrogen gas when carrying out
the hydrogen plasma process. The data shown in FIG.10 were obtained
at a pressure of 0.4 Torr using a microwave power of 500 W. As
shown in FIG.10, this experimental result also shows that the
density of hydrogen atoms increases when the ratio of water vapor
added to the hydrogen gas during the hydrogen plasma process is
greater than 0 and less than approximately 30%.
Therefore, according to the present invention, the hydrogen plasma
process is carried out using a first gas which includes hydrogen
molecules as the main component and a second gas which includes a
quantity of hydrogen smaller than that included in the first gas.
In the embodiments described above, the first gas is hydrogen gas
itself and the second gas is water vapor. However, the first and
second gasses are not limited to those of the embodiments. The
second gas may be a gas of organic compounds including hydrogen and
oxygen or inorganic compounds including hydrogen. In other words,
the second gas may include a material selected from a group which
includes alcohol, organic acid, phosphine (PH.sub.3), arsine
(ASH.sub.3), borane (BH.sub.3), diborane (B.sub.2 H.sub.6), water
vapor (H.sub.2 O), silane (SiH.sub.4) and ammonia (NH.sub.3). But
the second gas is preferably water vapor (H.sub.2 O) since it is
very easy to obtain and handle water, and further, because it is
possible to prevent undesirable carbon deposits on the chamber
wall, for example. Some materials when used as the second gas may
cause undesirable deposits on the chamber wall.
In addition, the surface which is to be subjected to the plasma
treating may be made of a material selected from a group including
organic materials, semiconductors and metals. In the case of an
organic material layer, this organic material layer before the
plasma treating is subjected to an energy particle irradiation such
as ion implantation, plasma and laser irradiation. The resist is a
typical example of the organic material, and the resist layer
before the plasma treating is preferably subjected to an ion
implantation with a dosage of 1.times.10.sup.14 atoms/cm.sup.2 or
greater and deteriorated. A semiconductor or metal layer may be
subjected to the plasma treating immediately before another layer
is formed on the semiconductor or metal layer. Si is a typical
example of the semiconductor, and a Si substrate is subjected to
the plasma treating before epitaxially growing a Si layer on the Si
substrate, for example. Al is a typical example of the metal, and
an Al layer is subjected to the plasma treating before forming
another Al layer on the Al layer, for example.
Further, the present invention is not limited to these embodiments,
but various variations and modifications may be made without
departing from the scope of the present invention.
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